With traditional extrusion a billet of material is pushed and/or drawn through a die to create a rod, rail, pipe, etc. Various applications leverage this capability. For instance, extrusion can be used with food processing applications to create pasta, cereal, snacks, etc., pipe pastry filling (e.g., meringue), pattern cookie dough on a cookie pan, generate pastry flowers and borders on cakes, etc. In another application, extrusion can be used with consumer goods, for example, to merge different colored toothpastes together on a toothbrush.
Micro extrusion involves the extrusion of fine featured (e.g., less than 50 micron width and height) structures on a target substrate. Extrusion heads for micro extrusion systems typically include metal plates that are laminated together using known high pressure wafer bonding techniques, with one or more of the plates being processed to define multiple fluidic channels that communicate with associated outlet orifices that are defined on an edge surface of the head. Extrusion material is inserted into fluidic channels through input ports such that the extrusion materials are shaped and extruded through outlet orifice, from which it is dispensed onto the target substrate.
Due to their fine structure, gridlines and other micro extruded structures produced by micro extrusion heads are extremely sensitive to variances in the fluidic channel shape and the distance of the outlet orifice from the substrate surface. In particular, most of the pressure drop typically occurs in the smallest and most constricted portions of the outlet and therefore variances in the outlet shape and distance can lead to a large variation in flow impedance for multiple orifice systems. Because the fluidic channels and outlet orifices are arranged in a relatively long line along the edge surface of the extrusion head, it is important that the edge surface of the extrusion head be as close to a perfect plane as possible. That is, slight imperfections in the head fabrication process that produce non-linearity along the edge surface, particularly at the outlet orifices, can result in non-optimal or even non-acceptable micro extruded structures.
Moreover, the methods used to form an extrusion head may introduce an unavoidable and often unpredictable shape change due to plastic deformation of the layers comprising the device, for example during high pressure bonding. Forming the orifices such that they have uniform flow impedance in situations where the orifice locations have shifted presents a fabrication challenge.
What is needed is an extrusion head for a micro extrusion system having a uniform orifice impedance such that the micro extruded structures formed by the extrusion head are consistent and reliable. What is also needed is a method for fabricating an extrusion head for micro extrusion systems that produces such a highly planarized edge surface.